U.S. Pat. No. 6,174,400 of Krutak et al. describes near infrared fluorescent security thermal transfer printing and marking ribbons. In this patent, the “prior art” is discussed, and it is disclosed that “ . . . thermal transfer ribbons incorporating invisible marking compound which are not visible to the unaided human eye . . . ” are not known. In such patent, the inventors disclose that, with regard to the infrared preferred embodiment (in which a near infrared fluorescer [NIFR] is incorporated into an ink composition), “When the positive image was viewed with a near IR camera designed for display of contrast images of the near IR fluorescence on a video monitor, a very faint image could be discerned . . . . The weakness of the image is due to carbon black absorption of most of the activating laser light and near IR fluorescence generated before it can exit the image surface. Use of black dye compositions, which do not absorb strongly in the near IR in place of the carbon black pigment results in stronger contrast images.”
The use of such “ . . . black dye composition which do not absorb strongly in the near IR . . . ” is still problematic inasmuch as such compositions generally still absorb in the visible range and, when used in combination with near infrared fluorescing taggants, produces a poor response from such taggants. It is an object of one embodiment of this invention to provide a system that enables strong black marks to be produced but also enables taggants in such system to respond well to excitation outside of the visible range to produce strong visible fluorescence.